The invention relates to imaging systems, and more particularly, to an acoustical imaging interferometer for detection of buried underwater objects.
Techniques enabling the detection of buried objects have a number of useful and important applications. For example, land mines and other such anti-personnel weapons remaining from past wars are a scourge in many countries. Likewise, sea mines present equally devastating hazards, and continue to deny coastal waters to fisherman and civilians. In time of war, military operations are also impeded or denied by the presence of mines.
Mines that are tethered below the water surface or standing proud on the seafloor can be detected by existing means or by systems in advanced development. Acoustical imaging methods are effective for tethered and proud mines even in very turbid littoral waters, where optical methods often fail. Low frequency sonar systems may also be employed and do not have the limitations of optical systems in turbid water. FIG. 1 provides a diagrammatic presentation of the relative turbidity versus resolution potential of conventional sonar, acoustical and optical imaging systems.
Many sea mines are designed to progressively bury themselves through the scouring action of water movement on the seafloor. Optical, sonar and conventional acoustical imaging systems are not effective for detecting such buried mines. In addition, many sea mines are constructed of non-magnetic or non-metallic materials such as fiberglass composites and are virtually undetectable by electromagnetic means. As a result, partially or completely buried mines, as well as other objects, remain difficult to detect.
What is needed, therefore, are techniques that enable the detection of buried underwater objects.
One embodiment of the present invention provides a system for detecting underwater buried (either partially or completely) objects. The system includes an acoustical camera that is adapted to produce three dimensional volumetric images of an underwater target area volume of an underwater floor. An acoustic transducer is adapted to apply an acoustic pulse to the target area volume so as to cause displacement of materials included in the target area volume. A controller is adapted to coordinate operation of the camera and the acoustic transducer, so that a volumetric image of the target area volume can be produced while the acoustic pulse is present in the target area volume. As such, buried objects can be detected based on relative movements in the target volume area. In one particular embodiment, a first volumetric image of the target area volume is produced before the acoustic pulse is applied, and a second volumetric image of the target area volume is produced while the acoustic pulse is present in the target area volume.
The controller can be further adapted to compare volumetric images for evidence of buried objects. The evidence of buried objects can be based, for example, on movement of floor materials relative to the buried objects. The camera may be configured to produce volumetric images of the underwater target area volume at a real-time frame rate, and may be further adapted to operate in an interferometer mode having a resolution of less than one wavelength. In one particular embodiment, the camera is configured for producing volumetric images within a 16 feet range at a frame rate greater than 10 frames/second, and has an acoustical lens configured for forming images on an array of acoustical transducer elements (e.g., piezocomposite).
The system may further include an image recorder that is adapted to record the volumetric images. The system may further include an image discrimination module adapted to discriminate interesting objects from non-interesting objects detected in the volumetric images. The system may further include a range finder that is adapted to detect when the system is at a proper distance from the target area volume for imaging purposes. Other variations will be apparent in light of this disclosure. For instance, note that the acoustical transducer can be extendible towards the target area volume (e.g., via operation of a mechanical arm).
Another embodiment of the present invention provides a method for detecting underwater buried (either partially or completely) objects. The method includes producing one or more three dimensional volumetric images of an underwater target area volume of an underwater floor, and applying an acoustic pulse to the target area volume so as to cause displacement of materials included in the target area volume. The method continues with producing one or more second volumetric images of the target area volume while the acoustic pulse is present in the target area volume. Producing volumetric images of the underwater target area volume may be performed at a real-time frame rate, and/or using a resolution of less than one wavelength.
The method may further include comparing volumetric images for evidence of buried objects. In one such embodiment, comparing volumetric images for evidence of buried objects includes detecting movement of floor materials relative to the buried objects. The method may further include recording the volumetric images. The method may further include discriminating interesting (e.g., man-made) objects from non-interesting (e.g., rocks) objects detected in the volumetric images. The method may further include detecting a proper distance from the target area volume for imaging purposes (e.g., based on camera range limitations). Note that not only can objects which are partially or completely buried be detected, but they can also be categorized, identified, or otherwise characterized.
The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter.